This application claims the priority of PCT patent application PCT/IB99/01776, filed Nov. 4, 1999, the disclosure of which is incorporated herein by reference in its entirety.
The present invention concerns a device for the production of optical lenses, in particular ophthalmic lenses, of polymerizable material.
Hitherto used methods for the manufacture of optical lenses comprises four steps, namely assembling a mold forming a cavity, filling said cavity with a molding material, polymerizing the molding material and removing the mold.
There are several optically acceptable materials known, e.g. the broadly used material called CR-39, a diethylene glycol bis (allyl carbonate) resin and CR 424, obtainable by PPG Industries, Inc., Pittsburgh, Pa. USA. Further materials are described in U.S. Pat. No. 5,880,171 (Lin et al.).
Also several filling methods are known such as e.g. described in U.S. Pat. Nos. 5,110,514 and 5,114,632 (both to Soane) and in U.S. Pat. Nos. 5,547,618 and 5,662,839 (of Magne).
For the mold also different systems are known. One system comprises two molding shells that are connected by an annular gasket surrounding them to form a mold with a cavity having the shape of the optical lens. This is the most classical method. The gasket, usually of thermoplastic material, insures the sealing of the two molding shells that have identical diameter and maintains them in the desired position (thickness, centering and prism). In general, a clip blocks the molding shells on the gasket.
The problem with this type of molding system is that
for each kind of lens, a different gasket has to be used, which implies complex management of a lot of tools,
the gasket usually is used only once and generally needs to be recycled to reduce costs.
The advantages of the gasket molding system are
the easiness to manually assemble the molding shells on the gasket,
the easiness to separate the lens from the mold when polymerization is achieved, namely e.g. with a spatula since the cavity formed by the molding shells and the gasket has a smaller diameter than the molding shells.
Another type of mold and method for making a lens is a method wherein the gasket is replaced by a tape. The mold in this quite popular method consists in two molding shells with identical diameter that are assembled not by a gasket but by surrounding the two molding shells on the edge by an appropriate tape. The tape, like the gasket, insures the sealing and the maintaining of the mold after positioning of the molding shells (thickness, centering and prism).
This method bears the disadvantage that
an automatic process has to be used (and thus developed) for positioning the molding shells and sticking the tape,
the molding shells cannot easily be removed by mechanical means, since they have exactly the same dimension as the lens.
Advantages of this method compared with the gasket method are that
with the same kind of tape, a lot of different geometries of lenses can be done,
the tape has relatively low volume and is available for relatively low costs, so: that no need to recycle said tape exists.
A further method is described in U.S. Pat. No. 5,547,618 and U.S. Pat. No. 5,662,839. Said method replaces the tape with two clamps that can be closed on the edge of the two molding shells having the same diameter. The two clamps, on their inner surface can be covered with a synthetic material.
The advantage of this system compared with the tape method is that no waste is generated since the sealing system is directly reusable. Furthermore all kind of geometries can be done as long as the same diameter is involved.
Disadvantages of this method are
the necessity to develop an automatic process for positioning the molds
the difficulty to separate the molding shell from the lens (see also xe2x80x9ctape methodxe2x80x9d above).
Furthermore, if reduction of the number of molds is desired, with the above described methods a blank has to be produced that then is mechanically adapted to the desired optical features. While in such a case a reduction of the number of different shells is achieved, such a method has the disadvantage that a lot of lens material is wasted.
Thus there is still a need for a molding system requiring less different molding shells or reducing the need for mechanical treatment, respectively, and allowing easy handling.
Hence, it is a general object of the present invention to provide a mold for producing optical lenses that, with the same parts, allows the production of several types of lenses.
Another object of the present invention is a method for producing optical lenses that uses said mold.
Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the mold is manifested by the features that it comprises
a gasket enclosing an aperture, which aperture extends along an axis, and providing a contact surface radially extending from said aperture,
a first molding shell abutting against said contact surface,
a second molding shell arranged within said aperture at a distance from said first molding shell,
at least one means for pressing said first molding shell against said contact surface,
at least one means for radially expanding said gasket or for radially pressing said gasket against said second molding shell or for radially expanding and radially pressing said gasket against said second molding shell, and
at least one filling opening,
thereby forming a molding cavity that can be filled with molding material between said first and said second molding shell and said gasket.
The mold for producing optical lenses of the present invention is primarily suitable for lenses made from a polymerizable synthetic material.
With the mold of the present invention it is furthermore possible to produce a broad variety of lens types with a minimum of molding shells. While the molding shells must be shaped for specific corrections such as monofocal lenses, multifocal lenses, progressive,lenses, toric lenses etc. or combinations thereof, with one: and the same pair of molding shells lenses of different thickness, dezentralization and prism can be formed.
Another aspect of the present invention is a method for the use of a mold of the present invention for the manufacturing of an optical lens from a polymerizable synthetic material comprising the steps of:
providing a mold within a molding device comprising a gasket enclosing an aperture, which aperture has an axis, and providing a contact surface radially extending from said aperture, a first molding shell and a second molding shell, at least one means for pressing said first molding shell against said contact surface of said gasket and at least one means for radially expanding said gasket or for radially pressing said gasket against said second molding shell or for radially expanding said gasket and for radially pressing said gasket against said second molding shell,
forming a molding cavity by performing the steps of
a) providing a gasket with an aperture whereby the surface of the cross section of said aperture perpendicular to said axis (further on also referred to as perpendicular surface) is larger than the projected area of said second molding shell projected in the direction of said axis (further on also referred to as projected area),
b) positioning said second molding shell in said aperture enclosed by said gasket,
c) radially clamping said second,molding shell in position by releasing a forced radial expansion of said gasket or by radially pressing said gasket against said second molding shell by means of said at least one radially pressing means or by releasing said forced radial expansion of said gasket and by radially pressing said gasket against said second molding shell by means of said at least one radially pressing means,
d)forming a molding cavity by pressing said first molding shell against said contact surface of said gasket by means of said at least one pressing means for said first molding shell,
whereby the steps a) to d) can be performed in the following sequences a) prior b) prior c) prior d), or a) prior d) prior b) prior c), or a) prior b) prior d) prior c), or d) prior a) prior b) prior c)
filling said molding cavity through a filling opening in said molding cavity with molding material,
performing at least partial polymerization of said molding material inside said molding cavity to form a lens,
disassembling the mold and
separating the lens.